Change Text, Button, and Icon on Button Click With Python in Blender
I got it batFINGER

Thanks! Mine was verbose indeed, but alas not close.

import bpy
from bpy.props import *

def initSceneProperties(scn):
    bpy.types.Scene.MyBool = BoolProperty(
        name = "Boolean", 
        description = "None")
    scn['MyBool'] = True
    return

initSceneProperties(bpy.context.scene)

class UIPanel(bpy.types.Panel):
    bl_label = "Property panel"
    bl_space_type = "VIEW_3D"
    bl_region_type = "UI"

    def draw(self, context):
        layout = self.layout
        scn = context.scene

        if scn.MyBool:
            icon = 'X_VEC'
            txt = 'Cancel'
        else:
            icon = "PAUSE"
            txt = 'Pause'

        layout.prop(scn, 'MyBool', text=txt, icon=icon, toggle = True)
        layout.label(text= txt)

bpy.utils.register_module(__name__)